An Evaluation of a Composite Model for Predicting Drop-Drop Collision Outcomes in Multidimensional Spray Computations

The standard model for predicting the outcome of drop-drop collisions in sprays is one developed based on measurements in rain drops under atmospheric pressure conditions. This model includes the possible outcomes of grazing collisions and coalescence. Recent measurements with hydrocarbon drops and at higher pressure (up to 12 bar) indicate the possibility of additional outcomes: bounce, reflexive separation and drop shattering. The measurements also indicate that the Weber number range over which bounce occurs is dependent on the gas pressure. The probability of a drop-drop collision resulting in bounce increases with gas pressure. A composite model that includes all these outcomes as possibilities is employed to carry out computations in a constant volume chamber and in a Diesel engine. A sub-model for bounce that includes the pressure effects is also part of the composite model. Comparisons of results obtained with the composite model are compared with those obtained with the standard model. Sauter-mean-diameter variations and mixing characteristics are studied under non-vaporizing, vaporizing and combustion conditions. It is shown that the probability of coalescence is noticeably reduced with the new model compared to the model based on the work of Brazier-Smith et al.